There are numerous efforts underway to generate renewable fuels from biomass (“biofuels”). One approach is to generate biodiesel fuel (predominantly fatty acid ethyl or methyl esters) from triglycerides. Another approach is to use the glycerol to form glycerol ethers, which can be added to biodiesel and/or diesel fuel. Still another approach is to convert cellulosic or starchy material to fermentable sugars, ferment the sugars to form alcohol, and add the alcohol to gasoline, such as E85 (an 85/15 ethanol/gasoline blend).
Each of these approaches is associated with certain limitations. To date, biomass has not been converted to hydrocarbons in the gasoline range, only biodiesel fuel, glycerol ethers, ethanol, and butanol. Since the majority of cars run on gasoline, this is a major limitation. Ethanol works fairly well as a gasoline additive, but the energy output in miles per gallon (“MPG”) is far lower for gasoline/alcohol blends than for gasoline.
In addition, yeasts have a limited ability to use sugars other than glucose. Glucose is only one of the sugars available from starch hydrolysis or from the depolymerization of cellulose or hemicellulose. Agricultural wastes such as corn stover and rice straw, and biomass crops such as switch grass or poplar trees, and even waste newspaper can all be converted into ethanol. However, a major limitation of these processes is that these feedstocks also include large amounts of other sugars, such as xylose, which yeast cannot easily metabolize.
In order to maximize the yield from biomass, it would be advantageous to provide fermentation processes that use sugars other than glucose. In order to facilitate adoption of alternative fuels, it would be advantageous to provide alternative fuels and fuel additives that can be used in the world's existing energy infrastructure. The present invention provides such processes and alternative fuels and fuel additives.